- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] A model theory question
by Alexander Solla 08 Oct '10

08 Oct '10

On Sep 30, 2010, at 1:39 AM, Patrick Browne wrote: > I think my original question can be rephrased as: > Can type classes preserve satisfaction under the the expansion > sentences > (signature/theory morphisms inducing a model morphism). > > According to [1] expansion requires further measures (programming?) > which you demonstrated. But this raises are further question. Does > Haskell’s multiple inheritance represent a model expansion where the > classes in the context of an instance are combined in the new bigger > model? In principle, the answer is yes (I think). But I kept running into walls when I tried. It is almost as if there is "too big" a gap to be filled between compile-time and run-time. At least for the approaches I tried. I have two suggestions though. First, monadism is a great way to approach this problem from a run-time level. Indeed, a monad is an interpreter, which comes with the associated notions of a free algebra/ model and the like. Injecting a new axiom amounts to creating a new monadic action. Monad transformers can do lifting and lowering in a fairly straight forward way. Another suggestion is to check out the OOHaskell paper. I know they use type level forcing to get stuff done, but I guess they used a different cluster of extensions than I tried. http://homepages.cwi.nl/~ralf/OOHaskell/ Sorry for the delay in responding. -Alex

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Is there a more recent paper or article than "Can GUI Programming Be Liberated From The IO Monad
by caseyh＠istar.ca 07 Oct '10

07 Oct '10

Is there a more recent paper or article than "Can GUI Programming Be Liberated From The IO Monad"? :)

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Notes from "Haskell takes over the world" BoF at ICFP
by Don Stewart 07 Oct '10

07 Oct '10

Here are the notes transcribed from the Future of Haskell BoF held after the Haskell Symposium last week. -- Don = Future of Haskell BoF Notes = A "birds of a feather" meeting was held at ICFP, organized by Bryan and Johan. We had 30 (?) people in a room, for 2 hours, discussing how to ensure Haskell succeeds. These are the transcribed notes. == Libraries == * Need to encourage special interest groups (SIGs) to form around particular domain areas in the libraries. AI, BioInf, Networking, etc. * Document the SIG process: what resources they have, how you get results. * Missing SIGs for certain platforms: Mac, CentOS etc. * More tutorials on use of Haskell in particular domains. * Keen for Hackage 2.0 quality review tools: embedded wikis, voting * Hackage analysis tools: reverse indexing of the code base. * There is no PVP tool. * Library fragmentation occuring due to type duplication (String, Text, ...) * Focus on intitiatives for common, core types. HP polish. * What is the "Son of Containers" going to be? * Build reports would help the community a lot. Integrated with Hackage. Haddock pages on hackage should be editable wikis (per-top-level function, dvcs backed? record history, captchas. roll back spam, by default assume good contributions) * Need to register patches to packages with lost maintainers. * Belgium Hackathon coming up. * Improve libraries process: esp. for small contributions. * Hackage maintainance: + maintainer timeout. + hackage package clobbering. + tweaks. hackage-local .cabal fixes. * Unclear what the rules for contributing are. Document them! * In particular, document how to contribute to: * ghc * cabal * core and HP * hackage * dockathon == IDEs == * A new ghci. + scriptable, scion-server? + repls on top of ghc-api + ruby repl + .ghci + documentation + hpaste/ghci. * IDE + scion. contributions. market places. + documentation. + EclipseFP, scion? + NetBeans. * Special Interest Groups + as the vehicle for domain projects. + formal process for forming a group. + a small amount of structure for groups + document process for forming a strike team. * haskell.org + polishing the wiki. + wikibooks. + call for sig. * haskell visual design group? + consistent color themes across haskell.org sites. + consistent haskell branding. * community server mailing lists in poor state * Move community more online ? Community services. + google groups + digests. + reply at the right point in the threads. + serious lists. + ghc users. libraries. + announces. + stackoverflow for new questions? + keep refering to SO. + reddit for news? == GHC == * ghc status + 50% split in room on moving ghc from darcs to git. + bug reports and interaction load with ghc + well documented workflow for lightweight changes + heavy weight process for major work. + bugs, tickets. + Simon Marlow "contributions are going up, and process is working well" * Release schedule. + RC at ICFP. + GHC release page. + HP/GHC release. + stage releases. + more clearly announced that ghc will be a beta prior to GHC HP. * HP, uses GHC installers as is. GHC zip. == Teaching / tutorials == * Tutorials. Documentation. + Writing a blog post that is wrong is a pretty good way to get feedback. + Find a forum to ask the question, so the answer is findable. + Ask on SO. + Clojure and Scala communities have active blog spheres. + they love descriptions of data structures + e.g. high fanout trees. + Aggregating the ephemera. + Archives: Haskell Reddit has all the interesting blog posts. -- Haskell Wikibook. * Cabal and integration with other languages. + Easier integration with C. + Higher barrier to entry on the Mac. + Playing well with other languages?

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HTML library with DOM?
by Günther Schmidt 07 Oct '10

07 Oct '10

Hi all, is there an HTML parsing library that creates a DOM from a page? Günther

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CFP MSCS Issue: Dependently Typed Programming
by Conor McBride 07 Oct '10

07 Oct '10

(s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)- >(p:P s)* OPEN CALL FOR PAPERS for a Special Issue of MATHEMATICAL STRUCTURES in COMPUTER SCIENCE in association with the workshop DEPENDENTLY TYPED PROGRAMMING 2010 editors: Thorsten Altenkirch (Nottingham), Conor McBride (Strathclyde) 2011 timeline: submission Jan 31; notification May 31; final version June 30 (s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)->(p:P s)*(s:S)- >(p:P s)* Thorsten Altenkirch and Conor McBride are delighted to invite contributions to a Special Issue of the journal Mathematical Structures in Computer Science (Cambridge University Press), in association with the Workshop on Dependently Typed Programming, which we organised on 9 and 10 July 2010 in Edinburgh, as part of FLoC, associated with LiCS. The workshop had a packed programme of exciting developments, reflecting the strength of work on this topic at this time. More recent workshops and conferences have exhibited a significant contribution from researchers in this area. We are grateful to Editor-in-Chief Giuseppe Longo and to Editor Eugenio Moggi for the opportunity to reflect these welcome developments in the pages of MSCS, and we encourage researchers to consider submitting a paper. submission deadline: January 31 2011 notification: May 31 2011 final versions due: June 30 2011 We invite full journal articles concerning Dependently Typed Programming or related topics, from authors at work in this area. Submissions are particularly welcome from but not limited to contributors to the workshop, and the same journal-standard peer review process will apply in any case. Please feel free to address any enquiries about scope and suitability to the guest editors, Thorsten Altenkirch (University of Nottingham) and Conor McBride (University of Strathclyde). Submissions should usually not exceed 35 pages. Authors should adhere to the guidelines issued by Cambridge University Press for MSCS contributors: http://assets.cambridge.org/MSC/MSC_ifc.pdf. These include directions to the relevant LaTeX resources. We very much look forward to hearing from you. Thorsten and Conor

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EDSL for Makefile
by C K Kashyap 07 Oct '10

07 Oct '10

Hi All, I was thinking about doing an EDSL for Makefile (as an exercise) I put down my line of thought here - http://hpaste.org/40233/haskell_makefile_edsl I'd appreciate some feedback on the approach. Also, I wanted some idea on how(in the current approach) I could make the target name and the dependency available to the action writer - as shown below. r1 = Rule { target = "file1", dependsOn = ["file2"], action = do execute ("gcc -c " ++ dependencyList ++ " -o " ++ target) } -- Regards, Kashyap

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Lazy evaluation from "Why Functional programming matters"
by C K Kashyap 07 Oct '10

07 Oct '10

Hi All, I was going through the paper's "lazy evaluation" section where the square root example is given. It occurred to me that one could implement it in a modular way with just higher order functions (without the need for lazy evaluation that is). function f (within, eps, next, a0){ while(true){ a1=next(a0); if(within(a0,a1,eps)return a0; a0=a1; } } Is this not the case? -- Regards, Kashyap

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Packaging a Gtk2hs based program for Windows
by Dmitry V'yal 07 Oct '10

07 Oct '10

Hello, haskellers. Recently I stumbled upon a problem. It may sound quite off-topic for this list, but, I'm sure, almost every haskell programmer runs into it sooner or later. It sounds: How to make a neat Windows installer for a nice Gtk2hs program I wrote last week? How to solve the problem of dependency on GTK? Should I ask my users to install a GTK package or it would be better to package all the dynamic libraries needed along with my program? Are there any troubles with different character encodings used in Windows? How to change the application icon? And so on.. I understand, there is no ultimate answer, but I hope there is some wisdom to share. I've been a Linux user for more then five years and now I've found myself completely illiterate on how to make my code easily accessible for a nontechnical Windows user. I would appreciate any thoughts and advises Best wishes, Dmitry

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Haskellers.com profiles: advice requested
by Michael Snoyman 07 Oct '10

07 Oct '10

Hi all, After finally getting OpenID 2 support worked out, I've now put up the Haskellers.com website[1]. Not all features are implemented yet, but the basics are in. One of the most important features is going to be the user profiles, and I wanted some community input on the kind of stuff they'd like to see. For now, I collect email address (spam-protected, don't worry), website, number of years of Haskell experience, and a free-form description. I've also added a skills section, but have purposely not added many. I wanted community input on the kinds of skills. Some ideas: * Web programming * Compiler writing * Write a monad tutorial :/ I see two main questions when it comes to selecting this list of skills: * How granular should we get? For web programming, for instance, should we ask about Yesod, Happstack, Snap, etc? * Should we include non-Haskell skills. I can imagine that employers would like to know that people also have experience with Java/C#/etc, but on the other hand we might want to make this Haskell-specific. One recommendation (from my wife actually) is to have two separate lists: a static list of Haskell-specific skills that users simply checkmark off, and then "additional skills" that everyone makes up themselves. Other things to consider for the profile: Twitter/Facebook/GChat/AIM accounts, Hackage username, list of packages authored. I'm also planning on adding a "real Haskeller" feature, which would mean a site admin (they don't exist yet) has verified that you really are a contributing member of the community. I would imagine the threshold for this status would be very low, eg you've written a package or sent email to one of the mailing lists. One last point: for those of you wondering why your profiles aren't showing up on the homepage: you need to verify your email address first. I just added this feature this morning which is why your profiles are not visible. This is simply an anti-spam measure. If it turns out to be insufficient, I might need to add a recaptcha, and if that is still not enough we can make things moderated. But I doubt spam will end up being a real problem. Cheers, Michael [1] http://www.haskellers.com/

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darcs vs. git
by Conrad Parker 07 Oct '10

07 Oct '10

(subject changed for easy filtering of flamebait, removed libraries@) On 7 October 2010 10:45, Jason Dagit <dagit(a)codersbase.com> wrote: > At the risk of starting a darcs vs. git discussion I have some > thoughts about the tension. > > On Wed, Oct 6, 2010 at 12:10 PM, Don Stewart <dons(a)galois.com> wrote: > [snip] >> == GHC == >> >> * ghc status >> + 50% split in room on moving ghc from darcs to git. > > I don't see that tension resolving itself easily. VCS tools are > subject to "network effects". If your friends are using VCS Foo and > you want to work with them, then you adopt Foo too. It's also a part > of the toolchain that people tend to have strong opinions about. > > One possible way to lessen the tension would be good vcs bridge tools. > There have been numerous repo converter projects, some even > supporting synchronization. There is already a git-svn tool. Maybe > there should be a git-darcs (and a darcs-git)? If a git hacker out > there wants to add darcs support to git, I'd certainly be willing to > help them get started. > > Pushing on this a bit more, I'm fairly convinced that darcs and git > are dual to each other in terms of underlying models. As such, I have > some ideas on how to unify them/convert between models. > Unfortunately, actually having something to use is very far off as the > ideas themselves are still immature. > > As far as I can tell, the main reasons to vote for git: > * Some people simply love git and want to use it for every project > * Git is faster and/or more memory efficient for some operations (most? all?) > * Github > > As far as I can tell, the main reasons to vote for darcs: > * GHC already uses it (inertia) > * The windows support appears to be more mature (I admit, this is > somewhat subjective as neither has a spotless record here) > * Key players, such as the Simons, prefer the darcs UI over the git > UI (i.e., some people prefer darcs) > * Darcs 2.x has consistently improved in robustness and efficiency > over the last several years, continues to improve, and incorporates > ideas from git. (there is currently an experimental 'rebase' command > in the development branch of darcs) > * Cherry picking > > Note: I didn't mention feature branches as a reason to prefer one over > the other. Both darcs and git support this. Git uses in-repo > branches and with darcs you can simply do a local lazy get. Some > people prefer one mechanism over the other, but the point is they both > support the workflow. I hope they do :) With darcs, is it possible to refer to various other (local and remote) branch names, eg. to do diffs between branches? What I mean is that with git, I can do: $ git fetch origin $ git diff my-foo origin/random-bar to see changes between my local branch "my-branch-foo" and the remote branch "random-bar" without having to make an explicit checkout of origin/random-bar. When the origin repo contains many branches that other people are working on, this is a pretty neat way of keeping track of those. I'd really like to be able to get an overview of what branches are available (on my local copy and remotely), like with git's various graphing tools; I just use a "git log --graph" alias to get a tree view in the console: http://blog.kfish.org/2010/04/git-lola.html Does something similar exist for darcs? > I would like to see the tension of darcs vs git for GHC reduced. I > think it ultimately amounts to: Contributors need to be able to use > the one they prefer, instead of being forced to use the one GHC devs > use. I agree with that, and I don't mind switching between the two for different projects. Perhaps some standard subcommand aliases would go a long way to making that easier though (log vs. changes etc.) cheers, Conrad.

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